1. Field of the Invention
The present invention relates to a high frequency electronic part and, in particular, to a high frequency module, such as a voltage control oscillator, a filter, an antenna duplexer, and an antenna module, which is used in the microwave band, the millimeter wave band, etc.
2. Description of the Related Art
As a result of the recent increase in the demand for mobile communications systems and the increase in the amount of information transmitted, the communication band for mobile communication is being expanded from the microwave band to the millimeter wave band. In constructing a dielectric filter, a voltage control oscillator (hereinafter referred to as "VCO") or the like is sometimes employed which includes a dielectric resonator (operating a TE01.delta. mode). The resonance frequency of an ordinary TE01 .delta. mode dielectric resonator is determined by an outer diameter of a cylindrical dielectric member. The coupling of the resonator with a micro strip line or the like is determined by the distance therebetween. Accordingly, a high level of accuracy in size and positioning is required.
In view of this, the present applicant has proposed, in Japanese Patent Application No. JP-A-7-62625, a dielectric resonator and a dielectric filter in which the above problem has been eliminated and which excel in machining accuracy.
In the dielectric resonator and the dielectric filter of the above-mentioned patent application, electrodes are formed on both main surfaces of a dielectric plate, whereby part of the dielectric plate is used as a dielectric resonator. In such a dielectric resonator, the electrodes formed on the dielectric plate can be used as a high frequency ground plane, so that, by forming a micro strip line on another dielectric sheet or the like and stacking it together with the dielectric plate, m it is possible to form a high frequency module, such as a VCO, including a dielectric resonator and an electronic part.
FIG. 9 is a sectional view of an example of the construction of such a high frequency module. In the drawing, numeral 1 indicates a dielectric plate on both main surfaces of which electrodes are formed. Numeral 2 indicates a dielectric sheet, on the upper surface of which wiring patterns 4 and 5 are formed and which has a through-hole th having a land P at a predetermined position. An electronic part in the form of a chip 28, is mounted on the land P. Wiring patterns 23 and 24 are connected to each other by a bonding wire w.
As shown in FIG. 9, by adopting a two-layered structure, composed of the dielectric plate 1 and the dielectric sheet 2, it is possible to use the electrode 15 on the dielectric plate 1 as a high frequency ground plane, forming the wiring patterns 4 and 5 on the dielectric sheet 2 as a micro strip line.
However, when mounting an electronic part, such as an FET, the ground connection of the electronic part is effected through through-hole th shown in FIG. 9, so that the grounding path becomes rather long, which may have an adverse effect on the high frequency characteristics. Further, since an electronic part in the form of a chip is mounted on the land having a through-hole, the structure is rather poor in heat radiation property, so that it cannot be applied to an electronic part in which a great quantity of heat is generated.
The above problem exists not only in the case in which a dielectric resonator is formed in a part of the dielectric plate 1, but is common to cases in which a dielectric sheet or the like is stacked on a base material having a high frequency ground surface to form a high frequency module.